Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Advances in battery technology have enabled the fabrication of tiny, high-energy-density electrochemical batteries capable of powering advanced devices for extended periods of time while occupying small volumes. An electrochemical battery comprises an electrolyte interposed between two electrodes (an anode and a cathode). Electrochemical reactions between the anode and the electrolyte and between the electrolyte and the cathode can cause the development of an electrical potential between the electrodes. Continued electrochemical reactions could drive an electrical current from one electrode, through a device connected to the electrodes, to the opposite electrodes, allowing the device to be powered by the electrical current.
Lithium ion batteries include a cathode and an anode separated from one another by an electrolyte that transfers lithium ions. During discharge, when the battery is providing current to a circuit connected across the electrodes, redox reactions occur at the two electrodes. Oxidation reactions at the anode ionize lithium, which releases electrons to the connected circuit from the anode, which causes a current to flow through the connected circuit from cathode to anode (i.e., reverse the direction of electron travel). Lithium ions are transferred through the electrolyte from the anode to the cathode to balance the flow of electrons in the circuit. At the cathode, the lithium ions and electrons are reduced. The difference in energy potential between the lithium when at the anode and at the cathode corresponds to the chemically stored energy in the battery. In some cases, lithium batteries may be re-charged by applying a reverse current to the electrodes, which causes lithium ions to traverse the electrolyte in the opposite direction, and to re-supply the anode with lithium.